Closed loop control of auxiliary injection unit

ABSTRACT

A method and apparatus of controlling commencement of an injection of a melt stream of moldable material from an auxiliary injection unit. A sensor is placed in an injection molding system to sense a condition related to an injection of a first melt stream of a first moldable material provided by a primary injection unit. Commencement of a second melt stream of a second moldable material from the auxiliary injection unit is initiated upon the sensed condition related to the injection of the first melt stream being detected at a preselected value. The sensed condition may be a pressure, velocity or temperature of the first melt stream as provided by a direct sensor, a force or strain on a hot runner component as provided by an indirect sensor or the occurrence of a function of the injection molding system as provided by a functional sensor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.14/222,259, filed Mar. 21, 2013, which is a continuation of U.S.application Ser. No. 13/034,165 filed Feb. 24, 2011, now U.S. Pat. No.8,715,547, both of which are incorporated by reference herein in theirentirety.

FIELD OF THE INVENTION

The invention relates generally to injection molding systems that havean auxiliary injection unit for co-injection or multi-materialapplications. More particularly, the invention relates to closed loopcontrol of the auxiliary injection unit.

BACKGROUND OF THE INVENTION

It is known in the art of injection molding to simultaneously orsequentially inject two melt streams of moldable material into a moldcavity using a single hot runner injection molding nozzle, which iscommonly referred to as co-injection. A first melt steam of a firstmoldable material may be provided by an injection molding machine, whichmay be referred to as a primary injection unit, while a second meltstream of a second moldable material may be provided by an auxiliaryinjection unit. The first and second melt streams are fed from theirrespective injection units into respective, separate first and secondmelt channels or runners of a manifold that are likewise in fluidcommunication with respective, separate first and second melt channelsof the nozzle through which the melt streams are directed to the moldcavity.

During a co-injection molding operation, controlling the flow of each ofthe first and second melt streams into the mold cavity is crucial inorder to produce consistent multi-layer parts. Conventionally, open loopcontrol of the molding process has been provided by which a signal orsuch may be sent by the primary injection unit to the auxiliaryinjection unit, the receipt of which triggers commencement of theinjection of the second melt stream by the auxiliary injection unit. Thetrigger signal may be set-up to permit sequential or simultaneousinjection of the first and second melt streams by the primary andauxiliary injection units. The drawback of open loop control is that itprovides no mechanism by which the actual molding conditions presentedby the flow of the first melt stream injected by the primary injectionunit may influence the commencement, speed and/or pressure of the flowof the second melt stream injected by the auxiliary injection unit.Without such real time closed loop control of the auxiliary unitinjection, co-injected molded parts may be produced that have layerswith inconsistent thicknesses and/or improper/undesirable relativepositioning.

Multi-material molding is another type of molding operation in which aprimary injection unit as well as an auxiliary injection unit are usedto supply the material required to make products, such as, toothbrushesthat have a handle made of a first harder material and a grippingsurface of a second softer material, and automotive lenses that have afirst color portion, e.g., a clear material, forming the main portion ofthe lens that has a void into which a second color portion, e.g., of anamber material, is molded. These types of multi-material moldingapplications may use a retracting core, called a “core pull” to create avoid into which the second material is injected. Other multi-materialoperations may use a rotary moving platen with multiple molding stationsthat mold various features onto a single product as each station engageswith a stationary half of the mold. In addition, spin stack molding inwhich a center block of a stack mold “flips” or rotates to engagedifferent faces of the center block with a stationary half of the moldto define different features of the part being molded is another waymulti-material overmolding is performed. In each multi-materialapplication, a first melt steam of a first moldable material may beprovided by an injection molding machine, while a second melt stream ofa second moldable material may be provided by an auxiliary injectionunit, such that, similar to the co-injection molding operation describedabove, controlling the flow of each of the first and second melt streamsinto the respective mold cavity is crucial in order to produceconsistent multi-material or co-injected molded parts.

As such, a need exists in the art for an injection molding system thatprovides real time communication of a condition of a first melt streamfrom a primary injection unit to provide synchronized or slavedinjection of a second melt stream from an auxiliary injection unit.

BRIEF SUMMARY OF THE INVENTION

Embodiments hereof are directed to a method and apparatus forcontrolling commencement of an injection of a melt stream of moldablematerial from an auxiliary injection unit. In an embodiment, a sensor ispositioned in an injection molding system to sense a condition relatedto an injection of a first melt stream of a first moldable materialprovided by a primary injection unit. Commencement of a second meltstream of a second moldable material from the auxiliary injection unitis initiated upon the sensed condition related to the injection of thefirst melt stream being detected at a preselected value, wherein thesensed condition may be a pressure, velocity or temperature of the firstmelt stream as provided by a direct sensor, a force or strain on a hotrunner component as provided by an indirect sensor, or the occurrence ofa function of the injection molding system as provided by a functionalsensor. In embodiments hereof, upon the sensed condition reaching thepreselected value, a signal is sent that either directly or indirectlyvia a time delay commences the injection of the second melt stream fromthe auxiliary injection unit.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other features and advantages of the invention will beapparent from the following description of embodiments thereof asillustrated in the accompanying drawings. The accompanying drawings,which are incorporated herein and form a part of the specification,further serve to explain the principles of the invention and to enable aperson skilled in the pertinent art to make and use the invention. Thedrawings are not to scale.

FIG. 1 is a schematic representation of a co-injection molding systemhaving closed loop control of an auxiliary injection unit in accordancewith an embodiment hereof.

FIG. 2 depicts a graph showing the relationship between a pressure orvelocity of an injection of a first melt stream of moldable materialfrom a primary injection unit and a pressure or velocity of an injectionof a second melt stream of moldable material from an auxiliary injectionunit over time as may be provided by the system of FIG. 1 in accordancewith a simultaneous co-injection embodiment hereof.

FIG. 3 depicts a graph showing the relationship between a pressure orvelocity of an injection of a first melt stream of moldable materialfrom a primary injection unit and a pressure or velocity of an injectionof a second melt stream of moldable material from an auxiliary injectionunit over time as may be provided by the system of FIG. 1 in accordancewith a sequential co-injection embodiment hereof.

FIG. 4 depicts a graph showing the relationship between the force/strainof an injection of a first melt stream of moldable material from aprimary injection unit on a hot runner component, and a pressure orvelocity of an injection of a second melt stream of moldable materialfrom an auxiliary injection unit over time as may be provided by thesystem of FIG. 1 in accordance with another simultaneous co-injectionembodiment hereof.

FIG. 5 depicts a graph showing the relationship between a pressure orvelocity of an injection of a first melt stream of moldable materialfrom a primary injection unit and a pressure or velocity of an injectionof a second melt stream of moldable material from an auxiliary injectionunit over time having preset time interval feedback adjustment of thesecond mold stream as may be provided by the system of FIG. 1 inaccordance with a simultaneous co-injection embodiment hereof.

FIG. 6 is a schematic representation of a multi-material injectionmolding system having closed loop control of an auxiliary injection unitin accordance with another embodiment hereof.

FIGS. 7A-7C depict exemplary preforms molded by co-injection methodsdescribed in embodiments hereof.

FIG. 8 depicts a graph showing the relationship between a pressure orvelocity of an injection of a first melt stream of moldable materialfrom a primary injection unit and a pressure or velocity of an injectionof a second melt stream of moldable material from an auxiliary injectionunit over time having injection stage feedback adjustment as may beprovided by the system of FIG. 1 in accordance with a simultaneousco-injection embodiment hereof.

DETAILED DESCRIPTION OF THE INVENTION

Specific embodiments are now described with reference to the figures.The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. In the following description, “downstream” is used withreference to the direction of mold material flow from an injection unitto a mold cavity of an injection molding system, and also to the orderof components or features thereof through which the mold material flowsfrom an injection unit to a mold cavity, whereas “upstream” is used withreference to the opposite direction. Although the description ofembodiments hereof is in the context of co-injection and multi-materialapplications of a hot runner injection molding systems, the inventionmay also be used in other molding arrangements where it is deemeduseful. Furthermore, there is no intention to be bound by any expressedor implied theory presented in the preceding technical field,background, brief summary or the following detailed description.

FIG. 1 is a schematic representation of an injection molding system 100.Injection molding system 100 includes a hot half 101 for directing meltfrom two separate melt sources S1, S2 to one or more mold cavities 106formed between hot half 101 and a cold half 103. As such, injectionmolding system 100 is a co-injection system that includes a primaryinjection unit 104 for providing a first melt stream of a first moldablematerial S1 to a mold cavity 106 and an auxiliary injection unit 102 forproviding a second melt stream of a second moldable material S2 to moldcavity 106. In accordance with an embodiment hereof, injection moldingsystem 100 includes closed loop control of auxiliary injection unit 102as described below. In an embodiment, primary injection unit 104 is aninjection molding machine and auxiliary injection unit 102 is anauxiliary injection unit that either is coupled to the injection moldingmachine or a mold held thereby or is disposed on a floor standpositioned next to the machine. In an alternate embodiment, an injectionmolding system in accordance herewith includes closed loop control ofmultiple auxiliary injection units.

Primary injection unit 104 feeds the first melt stream into a first setof hot runners or melt channels 108 of injection molding system 100 thatextend between a first inlet 107 and a mold gate 109 of mold cavity 106within hot half 101. Auxiliary injection unit 102 feeds the second meltstream into a second set of hot runners or melt channels 110 ofinjection molding system 100 that extend between a second inlet 111 andmold gate 109 of mold cavity 106 within hot half 101. It would beunderstood by one of ordinary skill in the art that the first and secondsets of hot runners 108, 110 are melt channels that may extend within orbe defined by various hot runner components, such as inlet or spruebushings 120, 120′, one or more manifolds such as manifold 122, and athermal or valve-gated nozzle such as thermally gated nozzle 124 orvalve-gated nozzle 124′, and that each of the first and second meltstreams separately flows through the various hot runner components tomeet proximate of or within mold cavity 106. Although a portion of firstand second melt channels 108, 110 are shown as extending within a singlemanifold 122 this is by way of illustration and not limitation. It wouldalso be understood by one of ordinary skill in the art that system 100is shown with only two mold cavities 106 for simplicity and that more orfewer mold cavities 106 may be positioned to receive the first andsecond melt streams provided thereby depending on the type and number ofmolded articles being produced and that an actual injection moldingsystem based on system 100 may have all thermally gated nozzles 124 orall valve-gated nozzles 124′ and not one or more of each as depicted byway of illustration in FIG. 1.

A sensor 114 is utilized within injection molding system 100 to allowclosed-loop operation between primary injection unit 104 and auxiliaryinjection unit 102. In the embodiment shown in FIG. 1, sensor 114 isattached proximate to first inlet 107 of the first set of runners 108.Sensor 114 is a direct melt stream sensor mounted to be in directcontact with the first melt stream flowing through runners 108 todirectly monitor a condition of the melt flowing therethrough. Sensor114 may be selected to monitor a condition of the melt stream such asthe pressure, temperature, or velocity of the first melt stream as itflows through the first set of runners 108. In an embodiment, sensor 114is one of a pressure or velocity sensor placed within first set of hotrunners 108 to obtain a direct reading of a respective condition of thefirst melt stream such as the pressure or velocity of the melt injectedby primary injection unit 104. In another embodiment, the sensor is atemperature sensor placed within first set of hot runners 108 to obtaina direct reading of a condition of the first melt stream such as achange in temperature attributed to shear heating of the melt as itflows through first set of hot runners 108 as a result of injection ofmelt by primary injection unit 104. In FIG. 1, the location shown forsensor 114 generally corresponds to a position along a melt channel ofrespective melt inlet or sprue bushing 120. In alternate embodimentshereof that are also shown in FIG. 1, sensor 114 may be disposedanywhere along the melt path of the first melt stream as it flows withinhot half 101 to include along a melt channel of manifold 122, asrepresented by sensor 114 a, or a melt channel of nozzle 124′, asrepresented by sensor 114 b. In another embodiment, a direct melt streamsensor is one of sensors 114 g, 114 g′ located on core plate 126 orcavity plate 128, respectively, in order to obtain a direct reading ofthe respective condition of the melt within mold cavity 106 duringinjection.

In another embodiment, an indirect sensor such as a force/strain gaugelocated at a point along an outer surface of a hot runner component maybe used in system 100 to provide closed-loop operation between primaryinjection unit 104 and auxiliary injection unit 102. Sensor 114 d thatis shown mounted on manifold 122 and sensor 114 e that is shown mountedon nozzle 124′ are indirect sensors in so much as they are disposed onan exterior surface of a hot runner component such as a nozzle,manifold, or inlet extension/sprue bushing to indirectly detect acondition of the first melt stream that is exhibited as a measurablemovement or change in the respective hot runner component. Themeasurable movement of the component, which may be a minor distortion orflexing of the injection molding system that occurs as a result of thepressurization of melt within first set of runners 108, is the sensedcondition detected by indirect sensor 114 d, 114 e that would indirectlyindicate the condition of the first melt stream being injected byprimary injection unit 104 without having to directly sense thecondition of the first melt stream.

In another embodiment, a functional sensor disposed within injectionmolding system 100 that detects the occurrence of a function withininjection molding system 100 may be used to provide closed loopoperation between primary injection unit 104 and auxiliary injectionunit 102. An example of a functional sensor includes a valve pinactuator position sensor 114 f associated with valve-gated nozzle 124′.Position sensor 114 f is disposed within system 100 to monitor afunction such as the activity of a valve pin actuator and subsequently avalve pin 130 coupled thereto as the actuator cycles between open andclosed positions for controlling the flow of the first melt streamprovided by primary injection unit 104 into mold cavity 106. As such,the sensed condition detected by functional sensor 114 f may be themovement of the valve pin actuator to a preselected position such as anopen or closed position.

Another example of a functional sensor includes a force/strain gaugemounted on or between the hot runner components of hot half 101, such assensor 114 c that is shown mounted on sprue bushing 120 proximatemanifold 122. Sensor 144 c measures or senses the force of a machinenozzle being brought into contact with sprue bushing 120. The locationof sensor 114 c shown in FIG. 1 may be particularly beneficial incertain injection molding applications in which the machinenozzle/carriage of primary injection unit 104 is retracted from hotrunner inlet 107 between each injection cycle. In another embodiment,sensor 114 c may be mounted on sprue bushing 120 proximate inlet 107.Examples of these types of injection molding applications include themolding of thin wall items and/or stack molding. In such applicationswhen the mold is opened in order to eject parts, the machine nozzle isretracted from inlet 107 to decompress the system so that melt droolfrom thermal gated nozzles 124 is minimized and/or to relieve shock onthe hot runner system during closure of the mold. In order to commencethe next injection cycle the mold is closed, wherein the machine nozzleis brought into contact with hot runner inlet 107, which is the sensedcondition detected by functional sensor 114 c, and the injection cycleof primary injection unit 104 commences.

Each of the above sensor locations as represented by sensors 114, 114a-114 g, 114 g′ would be suitable for co-injection molding applicationssuch as those used to mold a plastic bottle preform (as shown in moldcavity 106) where there is a middle layer of a barrier material providedby auxiliary injection unit 102 that is positioned between inner andouter layers of a skin material provided by primary injection unit 104.

In general, an injection of the first melt stream is commenced byprimary injection unit 104 and a condition of the melt flowing throughthe first set of runners 108 is monitored (either directly orindirectly) as described above by at least one of sensors 114, 114 a,114 b, 114 d, 114 e, 114 g, 114 g′. In addition, one or more functionsof injection molding system may instead or concurrently be monitored asdescribed above by at least one of sensors 114 c and 114 f. Continuousmonitoring of the condition of the melt and/or functions of injectionmolding system 100 by one of sensors 114-114 g′ permits auxiliaryinjection unit 102 to be slaved, in real time, to the actual output ofprimary injection unit 104. More particularly, when a preselected valuefor the sensed condition (direct or indirect) of the first melt streamis reached, and/or the occurrence of a function of injection moldingsystem occurs, a signal is sent to a controller 150 of auxiliaryinjection unit 102 to commence injection of the second melt streamrelative to an actual time, speed, and/or pressure of the first meltstream. In an alternate embodiment in an injection molding system inaccordance herewith, when a preselected value for the sensed condition(direct or indirect) of the first melt stream is reached, and/or theoccurrence of a function of injection molding system occurs, a signal issent to multiple controllers 150 of respective auxiliary injection units102 to commence injection of respective melt streams therefrom relativeto an actual time, speed, and/or pressure of the first melt stream.

In an embodiment, when a preselected value for the sensed condition(direct or indirect) of the first melt stream is reached and/or theoccurrence of a function of injection molding system occurs, a signal issent to controller 150 which will then start a timer 152 to delayinjection of the second melt stream by auxiliary injection unit 102 by apreset time period. The slaving of the commencement of the injection ofthe second melt stream provided by auxiliary injection unit 102 to thesensed condition(s) of the first melt stream by primary injection unit104 ensures that the start of the second melt stream is related to anactual time, speed, and/or pressure of the first melt stream.

FIG. 2 is a graph showing the relationship between a pressure “P” orvelocity “V” of the first melt stream of moldable material from primaryinjection unit 104 (“Inj P”) and a pressure “P” or velocity “V” of thesecond melt stream of moldable material from auxiliary injection unit102 (“Inj A”) over time “T” as may be provided by the system of FIG. 1in accordance with a simultaneous co-injection embodiment hereofFeatures and aspects of the other embodiments may be used accordinglywith the current embodiment. In this embodiment, when Inj P reaches apreselected pressure value P_(S) or preselected velocity value V_(S) assensed by one of direct sensor 114, 114 a, 114 b, 114 g, 114 g′, asignal will be provided to controller 150 of auxiliary injection unit102 to start Inj A. A delay of a time period “T₁” occurs betweencommencement of Inj P and commencement of Inj A that corresponds to thetime it takes the pressure P or velocity V of melt in the first meltstream to reach the preselected pressure value P_(S) or preselectedvelocity value V_(S). Inj P and Inj A continue for a time period “InjT.” Thereafter Inj P and Inj A are held over a sufficient time period toallow packing of mold cavity 106. It would be understood by one of skillin the art that injection pressure and velocity depend on shape, sizeand number of parts being molded and resins being used to mold the part.As well total injection time is not a set time but varies dependent onsuch variables as screw movement as well as shape, size and number ofparts being molded.

Referring to FIGS. 1 and 2 in the simultaneous co-injection embodimentdescribed above, when the preselected value of the sensed condition ofthe first melt stream is detected by at least one of direct sensor 114,114 a, 114 b, 114 g, 114 g′, the sensor sends a signal to controller 150that directly triggers commencement of the auxiliary unit 104. Inanother embodiment when the preselected value of the sensed condition ofthe first melt stream is detected by at least one of direct sensor 114,114 a, 114 b, 114 g, 114 g′, the sensor sends a signal to controller 150that triggers timer 152 that subsequently triggers commencement ofauxiliary unit 104 after passage of a preset time period. Similarly,indirect sensors 114 d, 114 e may be used to indirectly detect the startof melt flow from primary injection unit 104 by sensing a preselectedvalue of force or strain on a hot runner system component at which timea signal would be sent to controller 150 that would start melt flow fromauxiliary injection unit 104 at a time, speed, and pressure relative tothe first melt stream either immediately or after expiration of timer152.

FIG. 3 depicts a graph showing the relationship between a pressure P orvelocity V of a first melt stream of moldable material from primaryinjection unit 104 during a first and second injection cycle,represented by injection cycle profiles (1), (1′), and a pressure P orvelocity V of a second melt stream of moldable material from auxiliaryinjection unit 102 during an auxiliary injection cycle, represented byinjection cycle profile (2), over time T as may be provided by system100 of FIG. 1 in accordance with a sequential co-injection embodiment.Features and aspects of the other embodiments may be used accordinglywith the current embodiment. The depicted sequential injection cycleprofiles (1), (1′) and (2) shown in FIG. 3 are suitable for forming amolded article, such as, for example, a preform, having inner and outerlayers of a first material provided by primary injection unit 104 and amiddle or barrier layer of a second material provided by auxiliaryinjection unit 102. In this embodiment, when a first injection of thefirst material from primary injection unit 104 reaches a preselectedpressure value “P_(S)” or preselected velocity value “V_(S)” as sensedby at least one of direct sensor 114, 114 a, 114 b, 114 g, 114 g′, andas noted on injection cycle profile (1) that depicts the first injectionof an inner or outer layer of the molded article, than a signal will beprovided that actuates timer 152. After passage of a preset time period“T₁” that, in the current nonlimiting embodiment, ends just prior to thecompletion of the first injection, an injection of the second materialfrom auxiliary injection unit 102 commences, which is depicted byinjection cycle profile (2), to provide the middle or barrier layer ofthe molded article. In turn, after passage of a second time period “T₂”that ends just prior to the completion of the injection of the secondmaterial, the second injection of the first material from primaryinjection unit 104 is commenced, which is depicted by injection cycleprofile (1′), to provide an outer or inner layer of the molded article.

FIG. 4 depicts a graph showing the relationship between the force/strain(F/S) profile experienced by a hot runner component in injection moldingsystem 100 due to an injection from primary injection unit 104, which isrepresented by injection cycle profile (1), and a pressure or velocityprofile of a second melt stream of moldable material from auxiliaryinjection unit 102, represented by injection cycle profile (2), overtime T as may be provided by the system of FIG. 1 in accordance with asimultaneous co-injection embodiment. The depicted simultaneousco-injection profiles in FIG. 4 are suitable for forming a moldedarticle, such as, for example, a preform, having an inner and outerlayer of a first material provided by primary injection unit 104 and amiddle or barrier layer of a second material provided by auxiliaryinjection unit 102.

In the embodiment of FIG. 4, an injection of the first material fromprimary injection unit 104 produces a measurable amount of force/strainon injection molding system 100 which is exhibited as flex or distortionin one or more of inlet component 120, manifold 122, and nozzle 124.When an indirect sensor, such as a strain gauge, disposed on therespective surface thereof detects a preselected amount of force “F_(S)”or strain “S_(S),” as noted on injection cycle force/strain profile (1),which corresponds to the injection of a first melt stream of a firstmaterial that will form an inner and outer layer of the molded article,than a signal will be provided to controller 150 that actuates timer152. After passage of a preset time period T₁, an injection of a secondmelt stream of a second material from auxiliary injection unit 102commences, which is depicted by injection cycle pressure/velocityprofile (2), to provide the middle or barrier layer of the moldedarticle.

In embodiments of FIGS. 2-4 generally, the signal is sent to controller150 of auxiliary injection unit 102 as the monitored condition of thefirst melt stream (pressure, velocity, temperature, force, or strain)ascends to a preselected value suitable for initiation of injection ofthe second melt stream from auxiliary injection unit 102. It would alsobe understood by one of ordinary skill in the art that the preselectedvalue at which a signal is sent to controller 150 may happen at anypoint throughout the injection cycle such as when the monitoredcondition of the first melt stream (pressure, velocity, temperature,force, or strain) ascends to a preselected value, descends to apreselected value, or reaches a maximum or minimum preselected value.

In another embodiment, pressure P or velocity V of the first melt streamprovided by primary injection unit 104 may be measured after passage ofvarious intervals of time over the primary injection cycle to provideactive adjustment of the auxiliary injection in response to each sensedpressure P or velocity V. FIG. 5 depicts a graph showing therelationship between pressure P or velocity V of the first melt streamof moldable material from primary injection unit 104 represented byinjection cycle profile (1) and a pressure P or velocity V of the secondmelt stream of moldable material from auxiliary injection unit 102,represented by injection cycle profile (2) over time T having activeadjustment after each of preset time intervals “T_(i)” as may beprovided by the system of FIG. 1 in accordance with a simultaneousco-injection embodiment hereof Such an embodiment provides preset timeinterval feedback of a sensed condition of the first melt stream toauxiliary injection unit 102 upon which may be based adjustment of theinjection of the second melt stream such as would affect a pressure P orvelocity V of the second melt stream. Features and aspects of the otherembodiments may be used accordingly with the current embodiment.

Once injection of the first material from primary injection unit 104reaches a preselected pressure value P_(S) or preselected velocity valueV_(S) as sensed by at least one of direct sensor 114, 114 a, 114 b, 114g, 114 g′, a signal will be provided to controller 150 of auxiliaryinjection unit 102 to start injection of the second melt stream. A delayof a time period T₁ occurs between commencement of injection by primaryinjection unit 104 and commencement of injection of auxiliary injectionunit 102 that corresponds to the time it takes the pressure P orvelocity V of melt in the first melt stream to reach the preselectedpressure value P_(S) or preselected velocity value V_(S). Rather thansending a single signal to auxiliary injection unit 102 regarding whento commence injection of the second melt stream, controller 150 activelymonitors the pressure P or velocity V measurements provided by one ofdirect sensors 114, 114 a, 114 b, 114 g, 114 g′ after each specifiedtime interval T_(i), for example after a time interval of 0.1 seconds,starting from time T₁ that corresponds to commencement of the auxiliaryinjection as depicted in FIG. 5. From the commencement of injection byauxiliary injection unit 102, controller 150 takes a direct reading fromone of direct sensors 114, 114 a, 114 b, 114 g, 114 g′ at 0.1 secondintervals, for instance, and signals auxiliary injection unit 102 toactively adjust the pressure P or velocity V of the second melt streamas depicted by injection cycle profile (2) in response to the sensedcondition of the melt in the first melt stream at each interval asdepicted by injection cycle profile (2). Although the second melt streamdepicted by injection cycle profile (2) is shown as proportionatelyadjusted relative to the first melt stream depicted by injection cycleprofile (1) this is by way of illustration and not limitation.

FIG. 6 is a schematic representation of an injection molding system 600.Injection molding system 600 includes a hot half 601 for directing meltfrom two separate melt sources S1, S2 to one or more mold cavities 606a, 606 b formed between hot half 601 and a cold half 603. Injectionmolding system 600 is a multi-material injection molding system thatincludes a primary injection unit 604 for providing a first melt streamof a first moldable material S1 to a mold cavity 606 a and an auxiliaryinjection unit 602 for providing a second melt stream of a secondmoldable material S2 to mold cavity 606 b, in accordance with anembodiment hereof. Features and aspects of the other embodiments may beused accordingly with the current embodiment. Injection molding system600 includes closed loop control of auxiliary injection unit 602 asdescribed below. In an embodiment, primary injection unit 604 is aninjection molding machine and auxiliary injection unit 602 is anauxiliary injection unit that either is coupled to the injection moldingmachine or a mold held thereby or is disposed on a floor standpositioned next to the machine.

Primary injection unit 604 feeds the first melt stream into a first setof hot runners or melt channels 608 of injection molding system 600 thatextend between a first inlet 607 and a mold gate 609 a of mold cavity606 a within hot half 601. After the mold is rearranged, such as byretracting, rotating or spinning core plate 626 to provide mold cavity606 b, auxiliary injection unit 602 feeds the second melt stream into asecond set of hot runners or melt channels 610 of injection moldingsystem 600 that extend between a second inlet 611 and mold gate 609 b ofmold cavity 606 b within hot half 601. It would be understood by one ofordinary skill in the art that the first and second sets of hot runners608, 610 are melt channels that may extend within or be defined byvarious hot runner components, such as an inlet or sprue bushings 620,620′, one or more manifolds such as manifold 622, 622′, and a thermal orvalve-gated nozzle such as thermally gated nozzles 624 a, 624 b orvalve-gated nozzle 624 a′, 624 b′ and that each of the first and secondmelt streams separately flows through the various hot runner componentsto respective mold cavity 606 a, 606 b. Although a portion of first andsecond melt channels 608, 610 are shown as extending within separatemanifolds 622, 622′ this is by way of illustration and not limitation.In another embodiment a portion of first and second melt channels 608,610 extend separately within a single manifold as in the embodiment ofFIG. 1. It would also be understood by one of ordinary skill in the artthat system 600 is shown with only two mold cavities 606 a, 606 b toform only two multi-material parts for simplicity and that more or fewermold cavities 606 a, 606 b (not shown) may be positioned to receive thefirst and second melt streams provided thereby depending on the type andnumber of molded articles being produced. As well one of ordinary skillin the art would understand that an actual injection molding systembased on system 600 may have all thermally gated nozzles 624 a, 624 b orall valve-gated nozzles 624 a′, 624 b′ and not one or more of each asdepicted by way of illustration in FIG. 6.

A sensor 614 is utilized within injection molding system 600 to allowclosed-loop operation between primary injection unit 604 and auxiliaryinjection unit 602. In the embodiment shown in FIG. 6, sensor 614 isattached proximate to first inlet 607 of the first set of runners 608.Sensor 614 is a direct sensor mounted to be in direct contact with thefirst melt stream flowing through runners 608 to directly monitor acondition of the melt flowing therethrough. Sensor 614 may be selectedto monitor a condition of the melt stream such as the pressure,temperature, or velocity of the first melt stream as it flows throughthe first set of runners 608. In an embodiment, sensor 614 is one of apressure or velocity sensor placed within first set of hot runners 608to obtain a direct reading of the respective condition of the first meltstream such as a change in pressure or velocity attributed to injectionof melt by the primary injection unit 604. In another embodiment, sensor614 is a temperature sensor placed within first set of hot runners 608to obtain a direct reading of the respective condition of the first meltstream such as a change in temperature attributed to shear heating ofthe melt as it flows through first set of hot runners 608 as a result ofinjection of the first melt stream by primary injection unit 604. InFIG. 6, the location shown for sensor 614 generally corresponds to aposition along a melt channel of respective melt inlet or sprue bushing620. In alternate embodiments hereof that are also shown in FIG. 6, thedirect melt stream sensor may be disposed anywhere along the melt pathof the first melt stream as it flows within hot half 601 to includealong a melt channel of manifold 622, as represented by sensor 614 a, ora melt channel of nozzle 624 a′, as represented by sensor 614 b.

In another embodiment, the direct melt stream sensor is one of sensors614 g, 614 g′ located on core plate 626 or cavity plate 628,respectively, in order to obtain a direct reading of the respectivecondition of the melt within mold cavity 606 a, 606 b during injection.

In another embodiment the sensor may be an indirect sensor such as aforce/strain gauge located at a point along an outer surface of a hotrunner component, such as sensor 614 d that is shown mounted on manifold122 and sensor 614 e that is shown mounted on nozzle 624 a′. Sensors 614d, 614 e are indirect sensors in so much as they are disposed on anexterior surface of a hot runner component such as a nozzle, manifold,or inlet extension/sprue bushing to indirectly detect a condition of thefirst melt stream that is exhibited as a measurable movement or changein the respective hot runner component. The measurable movement of thecomponent, which may be a minor distortion or flexing of the injectionmolding system that occurs as a result of the pressurization of meltwithin first set of runners 608, is the sensed condition detected byindirect sensor 614 d, 614 e that would indirectly indicate thecondition of the first melt stream being injected by primary injectionunit 604 without having to directly sense the condition of the firstmelt stream.

In another embodiment, the sensor may be a functional sensor disposedwithin injection molding system 600 in order to detect the occurrence ofa function within injection molding system 600. An example of afunctional sensor includes a valve pin actuator position sensor 614 fassociated with valve-gated nozzle 624 a′ positioned to monitor afunction such as the activity of the valve pin actuator and concurrentlya valve pin 630 coupled thereto as the actuator cycles between open andclosed positions for controlling the flow of melt provided by primaryinjection unit 604 into mold cavity 606 a. As such, the sensed conditiondetected by functional sensor 614 f may be the movement of the valve pinactuator to a preselected position such as an open or closed position.

Another example of a functional sensor includes a force/strain gaugemounted on the hot runner components of hot half 601, such as sensor 614c that is shown mounted on sprue bushing 620 proximate manifold 622 suchthat the force of a machine nozzle being brought into contact with spruebushing 620 will be measured by sensor 614 c. The location of sensor 614c may be particularly beneficial in certain injection moldingapplications in which the machine nozzle/carriage of primary injectionunit 604 is retracted from hot runner inlet 607 between each injectioncycle. In another embodiment, sensor 614 c may be mounted on spruebushing 620 proximate inlet 607. Examples of these types of injectionmolding applications include the molding of thin wall items and/or stackmolding. In such applications when the mold is opened in order to ejectparts, the machine nozzle is retracted from inlet 607 to decompress thesystem so that melt drool from thermal gated nozzle 624 a is minimizedand/or to relieve shock on the hot runner system during closure of themold. In order to commence the next injection cycle the mold is closed,wherein the machine nozzle is brought into contact with hot runner inlet607, which is the sensed condition detected by functional sensor 614 c,so that the injection cycle of primary injection unit 604 may begin.Each of the above sensor locations represented by sensors 614, 614 a-614g and 614 g′ would be suitable for a multi-material molding applicationsuch as those used in molding automobile lenses, for instance.

A multi-material injection molding application in accordance withembodiment hereof may utilize functional sensor 614 f for triggering theinjection from auxiliary injection unit 102. More particularly,functional sensor 614 f is positioned to monitor the activity of anactuator and concurrently valve pin 630 coupled thereto as the actuatorcycles between open and closed positions for controlling the flow ofmelt provided by primary injection unit 604 into mold cavity 606 a. Inan embodiment, functional sensor 614 f is set to detect the openposition of the actuator associated with the first melt stream providedby primary injection unit 604. Upon detecting the actuator shifting toan open position a signal is sent to controller 650 to begin timer 652for initiation of a preset time period that includes a time period whichcommences at the completion of the primary injection cycle associatedwith primary injection unit 604 and during which the mold is altered tocreate mold cavities 606 b, such as by retracting the core orrotating/flipping the mold to align another mold part. After expirationof the preset time period, the secondary injection cycle commences fromthe auxiliary injection unit 602 to inject the second melt stream intothe mold cavities 606 b via second set of hot runners 610.

In general for embodiments described herein, one of sensors 114, 114a-114 g and 114 g′ of the embodiment of FIG. 1 and one of sensors 614,614 a-614 g and 614 g′ of the embodiment of FIG. 6, such as a pressuresensor 114, 614 positioned to directly sense a condition of the firstmelt stream injected by the respective primary injection unit 104, 604,transmits an analog signal (current or voltage, 0-10 v) to aprogrammable logic controller (PLC) 150, 650 of the respective auxiliaryinjection unit 102, 602. The PLC 150, 650 has an analog input card toconvert the analog signal to a digital signal that will either triggerthe auxiliary injection unit 102, 602 to commence an auxiliaryinjection, as described above, or start timer 152, 652 which will delaythe auxiliary injection by a preset time period.

In many cases, due to a lack of a machine language standard in theinjection molding industry, each time an auxiliary injection unit isincorporated into an existing injection molding machine there is acertain amount of customization of the injection molding machinecontroller that is necessary in order to enable communication betweenthe injection molding machine and the auxiliary injection unit. In othercases the auxiliary injection unit is triggered by a EUROMAP signal oran SPI signal provided by the injection molding machine. In either casean amount of customization, which is often time consuming, is involvedeach time an auxiliary injection unit is hard wired to an injectionmolding machine in order for the auxiliary injection unit to receive anoutput signal from the primary injection unit “telling” the auxiliaryinjection unit when to start. Although under ideal circumstances a starttime of an injection cycle by the auxiliary injection unit relative tocommencement of the injection cycle of the primary injection unit shouldbe generally constant, if a signal from the machine is relied on for thecommencement of injection by the auxiliary injection unit, any variancein the actual injection profile of the primary injection unit relativeto the programmed or desired injection profile may result in theauxiliary injection unit commencing either too soon or too late, whichmay cause inconsistent thicknesses and/or improper/undesirable relativepositioning of the two materials within the mold cavity.

An advantage of the use of sensors 114, 114 a-114 g or 114 g′ or sensors614, 614 a-614 g and 614 g′ as described in the embodiments above, theauxiliary controller 150, 650 of the auxiliary injection unit 102, 602need not be hard wired into the machine controller of the primaryinjection unit 104 providing a savings of time and eliminating the needfor customization, thereby making such systems in accordance withembodiments hereof readily adaptable to many injection moldingapplications.

In an embodiment a safety feedback sensor that can confirm that aninjection of the first melt stream by the primary injection unit 104,604 has actually occurred as a live injection may be useful inembodiments hereof, such as in cases where controller 150, 650 wouldwant to ensure that a live injection cycle had occurred prior to thetriggering of the injection by auxiliary injection unit 102, 602. Such asafety feedback sensor would ensure that the auxiliary injection unit102, 602 would not begin an injection of the second material when it isundesirable to do so. For example, although embodiments hereofcontemplate one of sensors 114, 114 a-114 g or 114 g′ or sensors 614,614 a-614 g and 614 g′ being used to provide closed-loop control betweenprimary injection unit 104, 604 and auxiliary injection unit 102, 602,two sensors may be used in conjunction with one another with the secondsensor serving as the safety feedback sensor. In a non-limiting example,a functional sensor, such as valve pin actuator sensor 114 f, 614 f,which is used to determine open and closed positions of an actuator,provides a signal to controller 150, 650 that is then used to provideclosed-loop control of the auxiliary injection unit 102, 602. Sincevalve pins can be actuated between open and closed positions at timeswhen no melt is being injected by primary injection unit 104, 604, suchas during set-up of injection molding system 100, 600 a safety feedbacksensor such as indirect sensor 114 e, 614 e can be used to monitor theforce/strain on nozzle 124, 624 such that auxiliary injection unit 102,602 is prevented from injecting unless the strain on nozzle 124, 624meets or exceeds a preset value indicative of a live injection ofprimary injection unit 104. In such a case, indirect sensor 114 e, 614 eacts as a safety feedback sensor by confirming that an injection hasbeen initiated.

FIGS. 7A-7C depict molded parts 770 a, 770 b, 770 c formed by anexemplary simultaneous co-injection molding application provided byinjection molding system 100 in accordance with embodiments hereof.Features and aspects of the other embodiments may be used accordinglywith the current embodiment. During set-up of injection molding system100 within an injection molding machine (not shown), an operator inputsinformation associated with making a specific part into both a userinterface of a machine controller (not shown) associated with primaryinjection unit 104 and a user interface of controller 150 associatedwith auxiliary injection unit 102. FIGS. 7A-7C depict forming 20 grampreforms 770 a, 770 b, 770 c for subsequent blow molding into a beveragecontainer or the like, having an inner and outer layer of PolyethyleneTerephthalate (PET) comprising 90% of the total part weight supplied byprimary injection unit 104, as well as a barrier layer of Ethylene VinylAlcohol (EVOH) comprising the remaining 10% of the total part weightsupplied by the auxiliary injection unit 102. In an embodiment, preforms770 a, 770 b, 770 c are molded in a mold having 32 cavities (not shown)and as such, the operator will provide input to the controller of theinjection molding machine that controls primary injection unit 104 toinject a shot volume of 576 grams (18 g×32). The operator will theninput into controller 150 to inject a shot volume of 64 grams (2 g×32).

With hot half 101 and cold half 103 of injection molding system 100urged together between the fixed and movable platen of an injectionmolding machine as would be understood by one of ordinary skill in theart, a first shot of melt is delivered to mold cavities 106 from primaryinjection unit 104 via first set of runners 108. As described in theembodiments above, at least one direct sensor 114, 114 a, 114 b, 114 g,and 114 g′ in communication with controller 150 is positioned todirectly sense a condition of the melt related to the injection of thefirst melt stream by primary injection unit 104. Once at least onedirect sensor 114, 114 a, 114 b, 114 g, and 114 g′ senses a preselectedvalue of the condition of the first melt stream, controller 150 sends asignal to auxiliary injection unit 102 to commence injection.Alternately, upon receiving the signal that the preselected value hasbeen reached, controller 150 will instead start timer 152 which will,after a programmed delay, send a signal to auxiliary injection unit 102to commence injection. Once primary and auxiliary injection units 104,102 have delivered their requisite shots of molding material to moldcavity 106, the newly molded articles are cooled within mold 106 untilthey have sufficiently solidified. Hot half 101 and cold half 103 arethen urged apart by the separation of the moving and fixed platen of theinjection molding machine, and the newly molded articles are thenejected from the mold. The machine operator will then inspect one ormore of the newly molded articles to evaluate the position of thebarrier layer within the inner and outer layer.

In an exemplary embodiment the preselected value for commencinginjection of the second melt stream by auxiliary injection unit 102 isthe detection of a pressure of 15,000 PSI by a direct sensor whichcorresponds to the start of the first melt stream flow from primaryinjection unit 104. The preselected value may be adjusted afterinspection of the molded preform either by incrementally changing thepreselected value for triggering the auxiliary injection by, forexample, +/−1000 PSI. or by setting timer 152 for 0.10 second incrementsto delay the auxiliary injection and thereby control the distribution ofthe barrier layer within the preform. In an alternate embodiment, apressure of 10,000 PSI is a preselected value for starting timer 152that is set for 0.50 seconds, for instance, and then after inspection ofthe molded preform the timer can be adjusted by, for example, +/−0.1second increments to control the distribution of the barrier layerwithin the preform.

If auxiliary injection unit 102 commences injection of melt too soon,there will be an uneven distribution of barrier material as shown bypreform 770 a in FIG. 7A, wherein the position P_(A) of the barriermaterial extends beyond a body of the preform and into a threaded regionwhere it is not needed. Upon viewing this scenario, the operator canprovide input to controller 150 to commence injection from the auxiliaryinjection unit 102 upon sensor 114 sensing a greater preselected value.Alternately, the operator may elect to activate injection-delay timer152 of controller 150 such that upon sensor 114 reaching the preselectedvalue, timer 152 will delay injection of the second melt stream byauxiliary injection unit 102. Conversely, if injection of the auxiliaryinjection material begins to late, there will be an uneven distributionin the gate and body region of the preform as shown at P_(B) of preform770 b in FIG. 7B. In this scenario, the operator can reduce thepreselected value at which sensor 114 signals auxiliary injection unit102 to commence injection. Alternatively, if timer 152 has been used todelay injection after the preselected value is reached, the operator canthen reduce the amount of elapsed time before a signal is sent tocommence injection by auxiliary injection unit 102. The result of suchadjustment capability is that the operator is given control over thecommencement of injection by auxiliary injection unit 102 relative tocommencement of injection by primary injection unit 104, such that thedistribution of barrier material within the inner and outer layermaterial may be readily adjusted until a desired preform product isproduced as shown at P_(c) of preform 770 c in FIG. 7C. Once thepreselected value, and if used, the time delay is optimized, thedistribution of barrier material within the inner and outer materialwill generally be consistently maintained through subsequent moldingcycles.

FIG. 8 depicts a graph showing the relationship between a pressure P ofthe first melt stream of moldable material from primary injection unit104 represented by injection cycle profile (1) and a pressure P of thesecond melt stream of moldable material from auxiliary injection unit102, represented by injection cycle profile (2), over time T havingpreselected injection stage feedback adjustment as may be provided bythe system of FIG. 1 in accordance with a simultaneous co-injectionembodiment hereof. Features and aspects of the other embodiments may beused accordingly with the current embodiment. In this embodiment, theinjection of the second melt stream of moldable material provided byauxiliary injection unit 102 is varied such as to affect a pressure Pthereof in response to a sensed condition of the first melt stream thatcorrelates to various stages of the injection cycle of primary injectionunit 104. For example, the injection of the second melt stream may beadjusted when the first melt stream has been sensed to have reached oneor more of a preselected maximum injection pressure value P_(MAX), aholding pressure value P_(HOLD), and a decompression pressure valueP_(DECOMP) are reached.

In an embodiment hereof, once injection of the first melt stream fromprimary injection unit 104 reaches a preselected pressure value P_(S) assensed by one of direct sensor 114, 114 a, 114 b, 114 g, 114 g′, asignal will be provided to controller 150 of auxiliary injection unit102 to start injection of the secondary melt stream. A delay of a timeperiod T₁ occurs between commencement of injection by primary injectionunit 104 and commencement of injection of auxiliary injection unit 102that corresponds to the time it takes the pressure P of melt in thefirst melt stream to reach the preselected pressure value P_(S). Ratherthan only sending a single signal to auxiliary injection unit 102regarding when to commence injection of the second melt stream, asdescribed in some of the embodiments above, controller 150 in accordancewith this embodiment continuously monitors the sensed condition of thefirst melt stream as provided by one of direct sensors 114, 114 a, 114b, 114 g, 114 g′ such that the injection cycle of auxiliary injectionunit 102 can be continuously varied or adjusted in real time in responsethereto at different stages of the injection cycle of primary injectionunit 104. In the embodiment shown, once a pressure of the first meltstream as depicted by injection cycle profile (1) reaches a preselectedmaximum injection pressure value P_(MAX), controller 150 sends a signalto auxiliary injection unit 102 to adjust the injection so as to reducea pressure of the second melt stream as depicted by injection cycleprofile (2) proportionately to that of the first melt stream. Inaddition or alternatively, once the direct sensor of primary injectionunit 104 senses the pressure of the first melt stream is at apreselected holding or packing pressure value P_(HOLD), controller 150signals auxiliary injection unit 102 to adjust the injection so as toincrease the pressure of the second melt stream to a value greater thanthat of the first melt stream and maintain that pressure until thedirect sensor of primary injection unit 104 senses the pressure of thefirst melt stream is reduced to a preselected decompression pressurevalue P_(DECOMP), such as during decompression of the system, at whichpoint controller 150 may again signal auxiliary injection unit 102 toadjust the injection so as to reduce the pressure of the second meltstream accordingly.

It would be understood by one of ordinary skill in the art that in viewof the disclosure hereof that the injection cycle profiles representedin FIGS. 2-5 and 8 are intended to be by way of example and notlimitation as to injection cycles contemplated by the present invention.In addition, it would be understood by one of skill in the art that inview of the disclosure hereof that the preselected value for signalingcommencement of auxiliary injection unit 102 could be measured andcorrelated at any point in the injection cycle of primary injection 104and not just during the increase in injection pressure shown oninjection cycle profile (1) in FIGS. 2-5 and 8. For instance withreference to FIG. 2 pressure P or velocity V of the primary injectionmay be measured after hitting peak pressure anywhere along the portionof injection cycle profile (1) where pressure and velocity aredecreasing.

While various embodiments have been described above, it should beunderstood that they have been presented only as illustrations andexamples of the present invention, and not by way of limitation.Although only one auxiliary injection unit is shown, more than oneauxiliary injection unit could be used with an injection molding systemif more than one auxiliary material is required by the specific moldingapplication. Also, it should be noted that although each of theembodiments describes an auxiliary injection unit used in conjunctionwith a molding machine with a primary injection unit, this is also byway of illustration and not limitation.

It will be apparent to persons skilled in the relevant art that variouschanges in form and detail can be made therein without departing fromthe spirit and scope of the invention. Thus, the breadth and scope ofthe present invention should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the appended claims and their equivalents. It will alsobe understood that each feature of each embodiment discussed herein, andof each reference cited herein, can be used in combination with thefeatures of any other embodiment. All patents and publications discussedherein are incorporated by reference herein in their entirety.

What is claimed is:
 1. A method of injection molding, the methodcomprising: monitoring a condition related to an injection of a firstmelt stream of moldable material from a primary injection unit having aprimary injection unit controller with a sensor in communication with asecondary injection unit controller; and signaling a secondary injectionunit with the secondary injection unit controller to adjust an injectionof a second melt stream of moldable material from the secondaryinjection unit in response to the monitored condition of the first meltstream.
 2. The method of injection molding according to claim 1, whereinthe monitoring the condition related to the injection of the first meltstream of moldable material comprises measuring the condition related tothe injection of the first melt stream at preset time intervals.
 3. Themethod of injection molding according to claim 1, further comprising:adjusting the injection of the second melt stream of moldable materialto be proportionate to the injection of the first melt stream ofmoldable material.
 4. The method of injection molding according to claim1, further comprising: determining different stages related to theinjection of the first melt stream of moldable material.
 5. The methodof injection molding according to claim 4, further comprising: adjustingthe injection of the second melt stream of moldable material in responseto the sensed condition of the first melt stream of moldable materialcorrelating to the different stages of the injection of the first meltstream of moldable material.
 6. The method of injection moldingaccording to claim 1, wherein the signaling the secondary injection unitwith the secondary injection unit controller to adjust the injection ofthe second melt stream comprises signaling the secondary injection unitwith the secondary injection unit controller to commence the injectionof the second melt stream of moldable material when the monitoredcondition related to the injection of the first melt stream of moldablematerial reaches a preselected value.
 7. The method of injection moldingaccording to claim 6, wherein the signaling the secondary injection unitwith the secondary injection unit controller to commence the injectionof the second melt stream of moldable material comprises signaling thesecondary injection unit when the monitored condition ascends to thepreselected value.
 8. The method of injection molding according to claim6, wherein the signaling the secondary injection unit with the secondaryinjection unit controller to commence the injection of the second meltstream of moldable material comprises signaling the secondary injectionunit when the monitored condition descends to the preselected value. 9.The method of injection molding according to claim 6, furthercomprising: forming a molded article having inner and outer layersprovided by the injection of the first melt stream of moldable materialand a middle layer provided by the injection of the second melt streamof moldable material; inspecting the molded article; and adjusting thepreselected value.
 10. The method of injection molding according toclaim 6, further comprising: delaying the signaling the secondaryinjection unit to commence the injection of the second melt stream ofmoldable material until after passage of a preset time period.
 11. Themethod of injection molding according to claim 10, further comprising:forming a molded article having inner and outer layers provided by theinjection of the first melt stream of moldable material and a middlelayer provided by the injection of the second melt stream of moldablematerial; inspecting the molded article; and adjusting the preset timeperiod.
 12. The method of injection molding according to claim 1,further comprising: monitoring a condition related to an injection of afirst melt stream of moldable material from a primary injection unithaving a primary injection unit controller with a second sensor incommunication with the secondary injection unit controller.
 13. Themethod of injection molding according to claim 12, wherein the secondsensor in communication with the secondary injection unit controllermonitors a second condition related to the first melt stream of moldablematerial.
 14. The method of injection molding according to claim 1,wherein the monitoring the condition related to the injection of thefirst melt stream of moldable material comprises monitoring a pressureof the first melt stream of moldable material.
 15. The method ofinjection molding according to claim 1, wherein the monitoring thecondition related to the injection of the first melt stream of moldablematerial comprises monitoring a temperature of the first melt stream ofmoldable material.
 16. The method of injection molding according toclaim 1, wherein the monitoring the condition related to the injectionof the first melt stream of moldable material comprises monitoring avelocity of the first melt stream of moldable material.
 17. The methodof injection molding according to claim 1, wherein the monitoring thecondition related to the injection of the first melt stream of moldablematerial comprises monitoring strain of a component related to the firstmelt stream of moldable material.
 18. The method of injection moldingaccording to claim 1, wherein the monitoring the condition related tothe injection of the first melt stream of moldable material comprisesmonitoring an occurrence of a function related to the injection of thefirst melt stream of moldable material.